Production companies use prop newspapers instead of real ones because getting clearance from an actual publication is usually more work than it's worth in potential fees and bureaucracy. (There are exceptions. When Tony Soprano picked up his paper each morning, it was always the Newark Star Ledger .) Rather than battle the legal department at the New York Times for that perfunctory breakfast shot, prop masters buy a stack of Earl Hays fake papers, which cost just $15 each. Sometimes if they have some left over they'll recycle them for another job.
Telephone numbers with the prefix 555 are widely used for fictitious telephone numbers in North American television shows, films, video games, and other media, although real numbers do exist in this range.